A Florida mother is speaking out after school officials sent a so-called "fat letter" saying her athletic 11-year-old daughter was overweight.

The child, Lily Grasso, stands 5 feet, 4 inches tall and weighs 124 pounds. After she underwent a mandatory health screening at her school in Naples, Fla., the Collier County Health Department sent a report to her family that classified her as overweight, Fox4Now.com reported.

Lily, a member of the school volleyball team, told wftv.com she was stunned and hurt by the letter:

"This whole thing is stupid. It's just not useful. It can hurt people. It can break their courage."

To her mother, Kristen Grasso, the evaluation sent a cruel message:

"To give a kid a letter telling them the rest of their life they may be overweight or be obese because of a measurement you took one day, it's just not fair."

Kristen Grasso disputes the label, telling Fox4Now: "Lily is tall, athletic, solid muscle. By no means is she overweight."

Not only that, but the report indicated Lily is 5 feet 3 inches, when she's closer to 5 feet 4, the Orlando Sentinel reported. That would yield a BMI putting Lily in the healthy range.

In any event, BMI is a poor tool for measuring obesity in children as muscular as Lily, the mother told the Sentinel in an email. She also criticized the process through which her daughter was evaluated:

"You want to measure Lily's health and development, then you better be a doctor who spends more than 3 seconds with her. Not a high school student helping administer health screenings."

Approximately 20 states have adopted BMI weigh-ins as part of mandatory health screenings designed to fight the childhood obesity epidemic, Yahoo!Shine reports.

Dr. Rexford Ahima, an obesity expert from the University of Pennsylvania, told Yahoo that BMI is the best, least costly tool available to identify at-risk children and is great for public health screenings. But it has drawbacks, too, he said, among them that it doesn't factor in variables such as ethnicity that could affect the result and it doesn't measure body fat vs. muscle. When it comes to individual children, he said, the child's doctor should be involved in the evaluation.

Some eating disorder experts tell ABCNews they worry that school obesity screenings may do more harm than good, especially to girls. Said Claire Mysko of the National Eating Disorders Association :

"I would like to see BMI testing in schools banned. For those who are already insecure about their weight, these tests can . . . potentially trigger an eating disorder."

Lily told ABC she was not going to let the letter get to her. Her plan, she said, was to "Be confident in everything that I do and never give up,"

Here's what "Good Morning America" had on the story:

What's your reaction to the letter and the Grasso family received? Please leave a comment below.